Organic light-emitting diodes (OLEDs), as current type light-emitting devices, have been increasingly applied in high performance display. With the increase of display size, traditional passive matrix organic light-emitting display (Passive Matrix OLED) requires every pixel to be driven in shorter time, larger transient current is required, thus power consumption is large. Meanwhile, application of large current may cause excess voltage drop on ITO line, and operation voltage of OLED is too high and thus operation efficiency thereof is decreased. Active matrix organic light-emitting display (Active Matrix OLED) can solve the above problem by progressively scanning currents inputted in the OLEDs by means of switch tubes.
In large-sized display application, since power supply lines of backboard have certain resistances and drive currents of all of the pixels are supplied by a power supply, power voltages of regions close to a power supplying position on the backboard is higher than those of regions away from the power supplying position. This phenomenon is called as internal resistance drop (IR drop). Since the voltage of the power supply has influence on current, the IR drop may cause difference in currents in different regions, and thus mura may be generated in display.
In addition, when forming an OLED through evaporation, non-uniformities in film thickness may cause non-uniformities in electrical performance. In the amorphous silicon (a-Si) or oxide thin film transistor process in which an N type thin film transistor is adopted to form a pixel unit, a storage capacitor is connected between a drive thin film transistor and an anode of a light-emitting diode, when data voltage is applied to gates of drive thin film transistors, since anodes of the light-emitting diodes of the pixel units have different voltages, Vgs(s), which are actually applied on the drive thin film transistors, are different, leading to different drive currents, and thus resulting in difference in actual display brightness.
The drive current may be calculated according to the following equation (1):
                                          I            OLED                    =                                    1              2                        ⁢                          μ              n                        ⁢                          C              ox                        ⁢                          W              L                        ⁢                                          (                                                      V                    data                                    -                                      V                    OLED                                    -                                      Vth                    n                                                  )                            2                                      ;                            (        1        )            
Wherein μn is carrier mobility of the nth OLED;
Cox is capacitance of a gate oxide layer;
  W  Lis width to length ratio of OLED;
Vdata is data voltage;
VOLED is operation voltage of OLED and is shared by all pixel units;
Vthn is threshold voltage of the nth drive thin film transistor, and is positive for an enhanced drive thin film transistor and negative for a depletion drive thin film transistor.
It can be seen from above that, if the drive thin film transistors of different pixel units are different in Vthn, the drive currents of the light-emitting devices in the pixel units are different, and if the Vthn of the drive thin film transistor of the pixel unit is drifted over time, the drive current thereof may be changed over time, resulting in ghost.
Therefore, how to avoid occurrence of mura, ghost, etc. when the display device is displaying becomes a problem to be solved urgently in the art.